One thousand two hundred eighty-one Zeiss DMC images were aerotriangulated to support digital ortho image production for Putnam and Dutchess counties, New York. Imagery and Airborne GPS data was provided by AERO-METRIC, Inc. Ground control and tie point data were provided by Vargis, LLC. The project was referenced to the North American Datum of 1983/1996 (NAD83/96), New York State Plane Coordinates, East Zone (3101) horizontally and to the North American Vertical Datum of 1988 (NAVD88) vertically. Units are in US Survey Feet. The DMC images (12 micron), ABGPS data, ground control, tie point, and camera data were used as inputs to the Zeiss/Intergraph ImageStation Automatic Triangulation (ISAT) softcopy program. ISAT was used to correlate image points and aerotriangulate the block of images to create exposure station exterior orientations. Where the software did not automatically correlate image points, image points were added manually.
Nineteen ground control points were manually measured on the imagery. These targeted point labels were prefixed with alpha characters (except the letter T). Of these nineteen control points, fourteen were marked with targets and the remaining four did not have identifications. One point did not have an existing target, but the imprint of a target was visible in the grass. For these four control points, the surveyed X and Y coordinates were used to locate their positions and only their Z coordinates were used in the adjustment. Twenty-three mapping tie points from adjacent counties (Columbia, Orange, Ulster, and Westchester) were also manually measured on the imagery. These tie point labels were prefixed with T2004. These tie points did not have identifications, but the client provided image clips that showed their approximate positions. Two of these mapping tie points (T20041384 and T20041434) were found to be under water and were not used.
Preliminary, the ground points were included in the aerotriangulation adjustment as unconstrained points for absolute ground location verification. In the final adjustment, the ground points were constrained. The targeted control points were held to 0.2 feet both horizontally and vertically. The non-targeted control points were held to 0.4 feet in vertical only. The mapping tie points were held to 2.0 feet horizontally and 1.0 foot vertically. The scale of the aerial photos is 1:25,400. The calibrated focal length for all of the imagery was 120.000 mm. The aerial photography was flown on 4-16-04. 1267 RGB DMC images were ortho-rectified and dodged using Z/I Imaging's OrthoPro. The input were the results from the Imagestation Automatic Triangulation (ISAT), the provided DTM/DEM data which was updated on DAT/EM Summit Evolution workstations and the 12 micron DMC images. Seamlines were drawn using Microstation and I_RAS C and imported into OrthoPro with the ortho-rectifications where
the images were then mosaicked, balanced and the final tile images cut out into TIFF/tfw format. The final images had look-up-tables (LUT) applied and the necessary fixes and bridge masks were done. Bridge deck data was collected on the softcopy stations for accurate horizontal placement. Final tile images were checked against the mapping and a few of the photo identifiable check points to assure accuracies were met